Numerous approaches are available to facilitate communication between programmable controllers or the like within a communication network. Some approaches utilize a communication topology wherein the programmable controllers are interconnected in a network having a ring configuration. With such a topology, if a fault occurs in a cable interconnecting the programmable controllers, the direction of communication is reversed so that communication is maintained via the other cables within the communication ring. For example, if communication is occurring in a clockwise direction between two programmable controllers in such a ring configuration and a fault occurs in one of the cables interconnecting same, communication automatically reverts to the counter-clockwise direction causing the data or information to pass through the cables which interconnect the other programmable controllers within the communication ring.
Another approach which ensures the continuity of communication between programmable controllers in a communication network involves the utilization of a plurality of cables to interconnect the controllers. Such approaches typically require the simultaneous communication over both the cables and the comparison of the incoming signals at the receiving programmable controller to determine which incoming signal should be selected. In this case, each incoming signal is typically compared against a preset value, and the signal which exceeds the preset value by a predetermined amount is selected. Alternatively, the signals can be compared against one another and the "stronger" signal selected. Since the incoming signal is not analyzed as to data integrity and/or the presence of noise, the possibility of forwarding faulty data or information to a receiving programmable controller exists.
In view of the foregoing, it has become desirable to develop a communication system which utilizes simultaneous communication over a plurality of cables and which analyzes the integrity of the data or information being received at the receiving programmable controller and selects the cable based on the integrity of the data or information being received, rather than incoming signal strength.